This section will dive into the technical specifications of the AI Agent Contract's execution. All content will focus on the off-chain components that allow for developers to host their Agent scripts or general purpose JS programs on Phala Network as a serverless backend.
The AI Agent Contract is served through Phala's gateway (https://wapo-testnet.phala.network/ipfs/\) and executes in a TEE compute node on Phala Network. Phala enables the execution of JS programs through a custom built WASM runtime called Wapo.
Wapo is a poll-based async WebAssembly runtime that provides extended networking support for guest WASM applications. It originated as a module called SideVM in Phala PRuntime, now independent, and the execution engine has been switched from wasmer to wasmtime.
Wapo is mainly designed as the next version of the AI Agent Contract execution engine. However, it can be used as a general-purpose WebAssembly runtime with networking support. The AI Agent Contract execution engine today is based on Substrate's pallet-contracts, which is not flexible enough and also has many limitations. Here is the table of comparison between 2.x and 3.0:
| AI Agent Contract 2.0 | AI Agent Contract 3.0 | |
|---|---|---|
| Program Type | WebAssembly | WebAssembly |
| VM Engine | wasmi | wasmtime (faster) |
| Incoming Networking | Query RPC | Query RPC or Listening on TCP port |
| Outgoing Networking | HTTP requests (with time and size limit) | Arbitrary TCP connections |
| Execution mode | Transaction/query-based, 10s limit | Long-running or query-based, no tx |
| App Memory | 4MB for ink / 16 MB for JS | Up to 4GB due to wasm32 limit |
With the enhancements with Wapo, Phala has taken the next steps to port the QuickJS implementation to execute in Wapo runtime called WapoJS.
WapoJS is an upgrade from the previous JS runtime called SideVM QuickJS. With this upgrade, developers can push the boundaries with their general-purpose JS programs with a faster response time vs the previous implementation.
| Feature | SideVM QuickJS | WapoJS |
|---|---|---|
| VM Memory | 16MB | 100MB (default) Up to 4GB |
| Maximum Execution Time | 60 seconds (default) to unlimited | 60 seconds (default) to unlimited |
| HTTP Request API | Asynchronous fetch API | Asynchronous fetch API |
| Websockets | Not Supported | Supported (not enabled, yet) |
| Concurrent Requests | Fully supported | Fully supported |
| Execution Speed | Fast | Faster |
| SCALE codec API | Sidevm.SCALE | Wapo.SCALE |
| Max Code Size | 500KB | Unlimited (Could be limited by streaming receiving from fetch + AbortController) |
| Limited CPU Burst | CPU time between async calls is limited. e.g. Too complex for-loop may hit the burst limit. | CPU time between async calls is limited. e.g. Too complex for-loop may hit the burst limit. |
For more information or inquries about increasing some resource limits, reach out the Phala Network team on discord.